incompetency vs unfitness

incompetency and unfitness both are nouns.

Word	Noun	Adjective	Verb	Adverb
incompetency	Yes	No	No	No
unfitness	Yes	No	No	No

As nouns, unfitness is a hypernym of incompetency; that is, unfitness is a word with a broader meaning than incompetency:

Other hypernyms of incompetency include inability.

incompetency (noun)	unfitness (noun)
lack of physical or intellectual ability or qualifications	the quality of not being suitable
	lacking the power to perform
	poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)